1. Field
The present innovations relate generally to methods and systems associated with locating weapon fire incident using sensor arrays. More specifically, innovations herein relate to techniques for locating the incident as a function of a combination of measured propagation phenomena including a discharge time.
2. Description of Related Information
Existing acoustic counter-sniper or gunshot/weapon discharge location systems sometime detect and locate gunshots by measuring the time of arrival of the muzzle blast on three or more time-synchronized microphones of known position. In some implementations, each acoustic sensor may have a single microphone capable of measuring time of arrival only; in other implementations each acoustic sensor may have multiple microphones, enabling each to measure both time of arrival and an angle of arrival in two (and sometimes three) dimensions. In some existing systems, two or more of such acoustic sensors may be combined to form an acoustic sensor array.
Drawback of such arrays include location accuracy limited by sensor array position and/or geometry. For example, three or four sensors may be sufficient to provide an accurate location when the shooter is confined within the convex hull defined by those sensors detecting the incident. As the shooter moves outside the polygon defined by the sensors, however, bearing accuracy (defined as the difference between the calculated and actual angle from the center of the array to the shooter) may remain acceptable but range accuracy (defined as the difference between the calculated and actual distance from the center of the array to the shooter) deteriorates. Graphically, a location solution can be constructed by intersecting linear azimuths of arrival from two or more sensors and/or hyperbolic lines of constant time difference of arrival from three or more pairs of sensors. The angle at which these lines intersect at the location is indicative of the quality of the range estimate, with a low angle indicating low accuracy and a high angle indicating high accuracy. As such, given an acoustic aperture λ as the width of the acoustic array perpendicular to the line from the array center to the shooter; for muzzle-only acoustic solutions, range accuracy begins to deteriorate as ρ\λ>2 where r is the actual range to the shooter (see, e.g., FIGS. 2 and 3).
To overcome this drawback, some gunshot location systems make additional use of the sound emitted by a supersonic projectile while it is in flight. Good estimates of shooter range can be obtained when a sufficient number bullet sound times and/or angles of arrival can be measured and an accurate ballistic model for the projectile is available. Such systems require that the projectile pass close enough to the acoustic sensor for the projectile noise to be detectable, and they are less suitable for use in urban situations where structures preclude detection of bullet sounds.
Other existing counter-sniper/gunshot location systems are based on detection of the muzzle flash, a bright flare of burning propellant emitted from the barrel of a weapon when it is discharged. However, such gunshot location system require a clear line of sight to the shooter's position. Furthermore, flash suppressors can reduce the intensity of light emitted by the muzzle flash, complicating detection. As with out-of-array location by acoustic sensor arrays, some optical systems may provide accurate bearing (direction) to the shooter but are less accurate at estimating range.
In still other existing systems, seismic sensors arrays are used to detect explosions, especially large explosions such as those created by underground testing of nuclear weapons. While certain overly complex and/or expensive seismic sensor networks can be used to locate the source of the explosion, the accuracy of seismic systems is dependent on the array geometry in a manner similar to acoustic systems.
In sum, there is a need for systems and methods that may accurately locate a weapon fire incident by, for example, using propagation phenomena including a discharge time obtained and/or processed via more advantageous arrangements of sensors or functionality.